#define  _CRT_SECURE_NO_WARNINGS

#include <stdio.h>

// 0!=1
//n! = 1*2*3*n

int main()
{
	int n = 0;
	int i = 0;
	int j = 0;
	int ret = 1;
	int sum = 0;
	scanf("%d", &n);

	for (i = 1;i <= n;i++)
	{

		ret *= i;
		sum += ret;
		
	}
	printf("%d\n", sum);
	return 0;
}